Methods for securing a cardiac tissue anchor

ABSTRACT

Devices and methods for securing a tissue anchor in tissue of a patient, in particular to ensure proper deployment of a cardiac tissue anchor by regulating the force or pressure of a deployment tool against the tissue. One way to ensure proper deployment force is to visualize the distal end of the tissue anchoring catheter from outside the body using a display for an imaging sensor, where the distal end of the catheter changes configuration when it is pressed against the tissue. Another method involves automatically regulating the pressure applied to the tissue prior to deployment of the tissue anchor, which may also be used in conjunction with visualization. Several safety locks to prevent deployment of the tissue anchor prior to establishment of the proper pressure are disclosed, which again may be used with visualization and/or an automated pressure regulator.

RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 16/107,718, filed Aug. 21, 2018, now U.S. Pat. No. 11,141,145,which claims priority under 35 U.S.C. 119 to U.S. ProvisionalApplication Ser. No. 62/550,361, filed Aug. 25, 2017, the contents ofwhich are expressly incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to devices and methods forsecuring a tissue anchor in tissue of a patient and, more particularly,to ensuring proper deployment of a cardiac tissue anchor by regulatingthe pressure of a deployment tool against the tissue.

BACKGROUND OF THE INVENTION

Heart valve disease, such as valve regurgitation, is typically treatedby replacing or repairing the diseased valve during open-heart surgery.However, open-heart surgery is highly invasive and is therefore not anoption for many patients. For high-risk patients, a less-invasive methodfor repair of heart valves is considered generally advantageous.

One solution is seen in U.S. Pat. No. 9,474,605 which discloses a heartvalve coaptation system for reducing regurgitation through a nativevalve. A flexible rail having a ventricular anchor on the distal endthereof adapted to anchor into tissue within a ventricle is firstdeployed. A delivery catheter has a lumen through which the flexiblerail passes, and a leaflet coaptation member is fixed on a distal end ofthe delivery catheter. Finally, a locking collet on the deliverycatheter secures the axial position of the coaptation member anddelivery catheter on the flexible rail. When in place, the coaptationmember reduces or eliminates regurgitation through the native valve, inparticular a tricuspid heart valve.

In order for systems similar to those disclosed in U.S. Pat. No.9,474,605 to properly function, the initial deployment of the flexiblerail is important, a lot of which depends on the location and securedeployment of the tissue anchor. There is a need for more reliableanchoring techniques.

SUMMARY OF THE INVENTION

The present invention relates generally to devices and methods forsecuring a tissue anchor in tissue of a patient, in particular to ensureproper deployment of a cardiac tissue anchor by regulating the force orpressure of a deployment tool against the tissue. One way to ensureproper deployment force is to visualize the distal end of the tissueanchoring catheter from outside the body using a display for an imagingsensor, where the distal end of the catheter changes configuration whenit is pressed against the tissue. Another method involves automaticallyregulating the pressure applied to the tissue prior to deployment of thetissue anchor, which may also be used in conjunction with visualization.Several safety locks to prevent deployment of the tissue anchor prior toestablishment of the proper pressure are disclosed, which again may beused with visualization and/or an automated pressure regulator.

System with Visibility Indicators

In one aspect, a system for ensuring secure anchoring of a tissue anchorwithin tissue in a patient's body using external visualization isdisclosed. The system has a tissue anchor deployment system including aproximal handle connected to an elongated flexible tube having a lumenwithin which translates an elongated tissue anchor tool with a distaltissue anchor thereon suitable for piercing and anchoring into tissue. Atissue contact indicator assembly configured to be visible from outsidethe body on a display for an imaging sensor is located adjacent a distalend of the flexible tube. The assembly has a movable member that in afirst position presents a first visual image on the display for theimaging sensor prior to contact between the distal end of the flexibletube and tissue, and presents a second visual image distinct from thefirst visual image after moving to a second position when apredetermined pressure is applied between the distal end of the flexibletube and the tissue. The predetermined pressure is calibrated to ensurethat the tissue anchor securely embeds into the tissue when the tissueanchor tool is subsequently advanced.

The movable member of the external visualization system may comprise adistal tubular housing having a relatively thin-walled body and a distalring that is thicker than the thin-walled body and consequently morevisible to the imaging sensor. The tubular housing is arranged to slideproximally within the flexible tube, and the flexible tube has a tubularhousing frame at a distal end with a relatively thick wall that isvisible to the imaging sensor, wherein proximal movement of the distaltubular housing causes the distal ring to move into proximity with thetubular housing frame and form the second visual image. In oneembodiment, the distal ring exhibits at least one chamfer or an outersurface that is uneven for greater visibility to the imaging sensor.Preferably, a spring is positioned between the tubular housing and theflexible tube which determines the predetermined pressure. In addition,a tensioner may be positioned intermediate the tissue contact indicatorassembly and the proximal handle which exerts a proximal force on theelongated tissue anchor tool, the tissue anchor having a size thatinterferes with a portion of the tubular housing so as to retract thetubular housing within the flexible tube.

Alternatively in the external visualization system, the movable membermay comprise a distal tubular housing having a first radiopaque bandthereon that is more visible to the imaging sensor than a remainder ofthe tubular housing. The tubular housing is then arranged to slideproximally within the flexible tube and the flexible tube has a secondradiopaque band thereon. The first visual image thus shows the first andsecond radiopaque bands spaced a first distance apart and the secondvisual image shows the first and second radiopaque bands closer togetherthan the first distance.

The external visualization system may further include a locking memberthat prevents movement of the movable member and is manually disengagedusing an actuator on the proximal handle. Also, the elongated tissueanchor tool may comprise a flexible rail affixed to the tissue anchor oris detachable from the tissue anchor. Desirably, the tissue anchor isselected from the group consisting of a plurality of distally-directedsharp tines having an outward elastic bias such that they curl outwardupon release from a surrounding constraint, and a corkscrew-like tine.

Ready to File System

Another system disclosed herein for ensuring secure anchoring of atissue anchor within tissue in a patient's body comprises a tissueanchor deployment system including a proximal handle connected to anelongated flexible tube having a lumen within which translates anelongated tissue anchor tool with a distal tissue anchor thereonsuitable for piercing and anchoring into tissue. A tissue contactpressure regulator assembly adjacent a distal end of the flexible tubehas a pusher shaft that is in a first position prior to contact betweenthe distal end of the flexible tube and tissue and is coupled to movewith the tissue anchor tool. The tissue contact pressure regulatorassembly includes a spring positioned between the pusher shaft and thedistal end of the flexible tube, such that after contact of the distalend of the flexible tube with tissue, initial advancement of the pushershaft to a second position displaces the tissue anchor tool to thedistal end of the flexible tube and compresses the spring to apply apredetermined pressure between the distal end of the flexible tube andthe tissue. Further advancement of the tissue anchor tool embeds thetissue anchor into the tissue, wherein the predetermined pressure iscalibrated to ensure that the tissue anchor securely embeds into thetissue when the tissue anchor tool is advanced.

In the ready-to-fire system, the spring may be fully compressed when thepusher shaft is in the second position and remains stationary duringfurther advancement of the tissue anchor tool. The distal end of theflexible tube may comprise a distal tubular housing having a relativelythin-walled body and a distal ring that is thicker than the thin-walledbody and consequently more visible to the imaging sensor. The tubularhousing is arranged to slide proximally within the flexible tube, andthe flexible tube has a tubular housing frame at a distal end with arelatively thick wall that is visible to the imaging sensor. Proximalmovement of the distal tubular housing thus causes the distal ring tomove into proximity with the tubular housing frame which is visible fromoutside the body on a display for an imaging sensor. The system mayfurther include a tensioner positioned intermediate the tissue contactpressure regulator assembly and the proximal handle which exerts aproximal force on the elongated tissue anchor tool, the tissue anchorhaving a size that interferes with a portion of the tubular housing soas to retract the tubular housing within the flexible tube.

The ready-to-fire system may further include a locking member thatprevents movement of the tubular housing and is manually disengagedusing an actuator on the proximal handle. Also, the elongated tissueanchor tool may comprise a flexible rail affixed to the tissue anchor oris detachable from the tissue anchor. Desirably, the tissue anchor isselected from the group consisting of a plurality of distally-directedsharp tines having an outward elastic bias such that they curl outwardupon release from a surrounding constraint, and a corkscrew-like tine.

In the ready-to-fire system the spring may be a coil spring positionedaround a narrow distal end of the pusher shaft that engages the flexibletube and compresses as the narrow distal portion passes through theflexible tube.

In any of the systems described herein, a guide balloon may bepositioned around the distal end of the flexible tube that helps prevententanglement of the distal end of the flexible tube with anatomicalstructures.

Removable Lock

A third system for ensuring secure anchoring of a tissue anchor withintissue in a patient's body comprises a tissue anchor deployment systemincluding a proximal handle connected to an elongated flexible tubehaving a lumen within which translates an elongated tissue anchor toolwith a distal tissue anchor thereon suitable for piercing and anchoringinto tissue. A tissue contact pressure regulator assembly adjacent adistal end of the flexible tube has a locking member that has a firstposition that prevents advancement of the tissue anchor tool and isdisplaceable to a second position that permits advancement of the tissueanchor tool. When the distal end of the flexible tube is pressed againsttissue, the pressure regulator assembly applies a predetermined pressurebetween the distal end of the flexible tube and the tissue. Thepredetermined pressure is calibrated to ensure that the tissue anchorsecurely embeds into the tissue when the locking member is displaced tothe second position and the tissue anchor tool is advanced into thetissue.

A further understanding of the nature and advantages of the presentinvention are set forth in the following description and claims,particularly when considered in conjunction with the accompanyingdrawings in which like parts bear like reference numerals.

BRIEF DESCRIPTION OF THE DRAWINGS

To further clarify various aspects of embodiments of the presentdisclosure, a more particular description of the certain embodimentswill be made by reference to various aspects of the appended drawings.It is appreciated that these drawings depict only typical embodiments ofthe present disclosure and are therefore not to be considered limitingof the scope of the disclosure. Moreover, while the figures may be drawnto scale for some embodiments, the figures are not necessarily drawn toscale for all embodiments. Embodiments of the present disclosure will bedescribed and explained with additional specificity and detail throughthe use of the accompanying drawings.

FIGS. 1A and 1B are cutaway views of the human heart in a systolic phaseshowing introduction of an anchoring catheter into the right ventricleas a first step in deploying a device for reducing tricuspid valveregurgitation;

FIG. 1C is a cutaway view of the human heart after securing a tissueanchor in the right ventricle and then advancing a device for reducingvalve regurgitation into position within the tricuspid annulus over anelongated tissue anchor rail;

FIG. 2A is an exploded view of a tissue anchor (shown partly in section)along with an assembly of components on the distal end of the anchoringcatheter for regulating the pressure of the catheter against tissueincluding an internal spring member, and FIG. 2B is an assembled view ofthe pressure regulating assembly;

FIGS. 3A-3D are sectional views of steps in positioning an exemplarytissue anchoring catheter over a target tissue site;

FIGS. 4A-4E are sectional views of steps of repositioning the tissueanchoring catheter and then deploying the tissue anchor into the tissueusing the pressure regulating assembly;

FIG. 5 is an exploded view of an alternative pressure regulatingassembly of components for use on the distal end of a tissue anchoringcatheter also having an internal spring and calibrated so thatdeployment of the tissue anchor is semi-automated;

FIGS. 6A and 6B are sectional views of the alternative pressureregulating assembly showing removal of a lock preventing advancement ofthe tissue anchor, and FIGS. 7A and 7B are schematic views ofalternative locks;

FIGS. 8A-8D are sectional views of steps in positioning a furtheralternative tissue anchoring catheter over a target tissue site which isa hybrid that combines pressure regulation an automatic tissue anchordeployment with visualization;

FIGS. 9A-9C are sectional views of steps of deploying the hybrid tissueanchor into the tissue using a pressure regulating assembly having anautomatic deployment arrangement and visible indicators;

FIGS. 10A-10B are schematic views of the distal end of a tissueanchoring catheter of the present application showing differentfluoroscopic images visible using an external imaging sensor of twopositions of the pressure regulating assembly;

FIGS. 11A-11C are schematic views of different fluoroscopic imagesvisible on an external imaging sensor of an alternative pressureregulating assembly in different positions;

FIGS. 12A-12B are schematic views of fluoroscopic images visible on anexternal imaging sensor generated by a further alternative pressureregulating assembly;

FIGS. 13A and 13B are perspective views of distal ends of tissueanchoring catheters showing alternative echogenic tips for high externalvisibility;

FIGS. 14A-14C are elevational views of alternative springs that may beused in the tissue anchor catheter pressure regulating assemblies;

FIGS. 15A-15E are sectional views of still further alternative springsformed by flexible plunger-like structures on the distal end of thetissue anchor catheter that deform upon contact with tissue and may alsoact as visual indicators;

FIGS. 16A-16C are sectional and elevational views of an alternativepressure regulating assembly for the tissue anchor catheters of thepresent application that utilizes an external braided structure thatexpands radially outward when axially compressed;

FIGS. 17A and 17B illustrate an alternative pressure regulating assemblyincluding an internal bellows-like structure in two different positions,and FIG. 17C shows an internal spring that may incorporate radiopaquemarkers;

FIG. 18A is a schematic view of the distal end of an exemplary tissueanchor catheter of the present application showing extension ofspring-loaded tip, and FIG. 18B is a schematic view of a preferredretracted position of the spring-loaded tip during delivery;

FIGS. 19A and 19B are schematic views of two different solutions forenabling retraction of the spring-loaded tip as in FIG. 18B;

FIG. 20A is an elevational view of an alternative positioning balloonfor use on the distal end of the tissue anchor catheter which isinverted to reduce the extent of the catheter that projects distallyfrom the balloon, and FIG. 20B is a sectional view through one sidewallof the tissue anchor catheter of FIG. 20A;

FIG. 21A is a perspective view of a partial implant of an annuloplastyring around a mitral annulus using the techniques described herein, andFIG. 21B shows the annuloplasty ring fully implanted;

FIG. 22 shows one exemplary tool for installing a tissue anchor that canbe used to implant the annuloplasty ring as seen in FIGS. 21A and 21B;

FIGS. 23A and 23B are sectional views through a sleeve-like annuloplastyring showing use of the tool of FIG. 22 to install tissue anchors; and

FIGS. 24A-24C are sectional views of steps in utilizing an exemplarytissue anchoring catheter through the sleeve-like annuloplasty ring toinstall one of the anchors.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description refers to the accompanying drawings, whichillustrate specific embodiments of the invention. Other embodimentshaving different structures and operation do not depart from the scopeof the present invention.

Various embodiments of the present disclosure are directed to devicesand methods for ensuring accurate placement and secure deployment of atissue anchor, in particular for a tissue anchor embedded in an internalwall of the heart. For instance, U.S. Pat. No. 9,474,605 (expresslyincorporated herein) discloses systems that require anchoring deviceswithin the wall of the left or right ventricle. Visualization such asvia fluoroscopy helps with locating the tissue anchor within theventricle, but by itself cannot inform the operator whether the tissueanchor has contacted the internal ventricular surface with sufficientforce. Tissue anchors that embed themselves within tissue may notpenetrate far enough into the tissue if the deployment catheter is notpushed against the target tissue with adequate force. Conversely,excessive force may cause damage to the tissue surface or even cause anunwanted puncture through a tissue wall. The same problems anchoringdevices within the heart ventricles arise for tissue anchors deployed inother internal body cavities, and the present application should not beconsidered limited to cardiac tissue anchors. To explain the solutionsdisclosed herein in the context of cardiac tissue anchors, anunderstanding of the internal anatomical structures of the heart isprovided first.

FIGS. 1A and 1B are cutaway views of the human heart in diastolic andsystolic phases, respectively. The right ventricle RV and left ventricleLV are separated from the right atrium RA and left atrium LA,respectively, by the tricuspid valve TV and mitral valve MV; i.e., theatrioventricular valves. Additionally, the aortic valve AV separates theleft ventricle LV from the ascending aorta (not identified) and thepulmonary valve PV separates the right ventricle from the pulmonaryartery (also not identified). Each of these valves has flexible tissueleaflets extending inward across the respective orifices that cometogether or “coapt” in the flowstream to form the one-way fluidoccluding surfaces. The regurgitation reduction devices of the presentapplication are primarily intended for use to treat the atrioventricularvalves, and in particular the tricuspid valve. Therefore, anatomicalstructures of the right atrium RA and right ventricle RV will beexplained in greater detail, though it should be understood that thedevices described herein may equally be used to treat the mitral valveMV with an anchor placed in the left ventricle LV.

The right atrium RA receives deoxygenated blood from the venous systemthrough the superior vena cava SVC and the inferior vena cava IVC, theformer entering the right atrium above, and the latter from below. Thecoronary sinus CS is a collection of veins joined together to form alarge vessel that collects deoxygenated blood from the heart muscle(myocardium), and delivers it to the right atrium RA. During thediastolic phase, or diastole, the venous blood that collects in theright atrium RA is pulled through the tricuspid valve TV by expansion ofthe right ventricle RV. In the systolic phase, or systole, seen in FIGS.1A and 1B, the right ventricle RV collapses to force the venous bloodthrough the pulmonary valve PV and pulmonary artery into the lungs.During systole, the leaflets of the tricuspid valve TV close to preventthe venous blood from regurgitating back into the right atrium RA. It isduring systole that regurgitation through the tricuspid valve TV becomesan issue, and the devices of the present application are beneficial.

FIGS. 1A and 1B show introduction of a tissue anchoring catheter 20 intothe right ventricle as a first step in deploying a device of the presentapplication for reducing tricuspid valve regurgitation. The catheter 20includes an outer sheath 22 defining an internal lumen through whichpass a tissue anchor 24 (see FIG. 1C) and anchor rail 26. The anchoringcatheter 20 enters the right atrium RA from the superior vena cava SVCafter having been introduced to the subclavian vein using well-knownmethods, such as the Seldinger technique. A guide balloon 28 adjacentthe distal end of the catheter 20 assists passage through the leafletsof the tricuspid valve TV and helps reduce the occurrence of chordalentanglement. The balloon is inflated in the right atrium RA and is thendeflated once the anchoring catheter 20 has reached the right ventricle.The physician advances the anchoring catheter 20 until its distal tip istouching the target anchoring site within the right ventricle, as seenin FIG. 1B.

FIG. 1C shows the tissue anchor rail 26 after installing the tissueanchor 24 at the apex of the right ventricle RV. The tissue anchor 24and anchor rail 26 were expelled distally from within the cathetersheath 22, and the tissue anchoring catheter 20 has desirably beenremoved completely from the patient's body in favor of a second catheter40. Preferably, the catheter 40 has a central lumen and advances overthe anchor rail 26. The operator positions a spacer or coapting member42 mounted on the second catheter 40 within the leaflets of thetricuspid valve TV. Various configurations of coapting members 42 areknown in the art, in particular as disclosed in U.S. Pat. No. 9,474,605.The second catheter 40 is desirably locked in position on the anchorrail 26 such that the coapting member 42 remains between the tricuspidvalve leaflets. The presence of a coapting member 42 is intended to fillany gaps between the tricuspid valve leaflets which might result inregurgitation, and thus function something like a plug between theleaflets.

The exemplary tissue anchor 24 includes a plurality of circumferentiallydistributed and distally-directed sharp tines or barbs 30 that piercethe tissue of the ventricular apex. The barbs 30 are held in a stressedconfiguration within the sheath 22, and are provided with an outwardelastic bias so that they curl outward upon release from the sheath.Desirably the barbs 30 are made of a super-elastic metal such asNitinol. The outward curling of the barbs 30 is caused by the elasticmaterial reverting to its relaxed configuration, the barbs 30 beingpreviously held in a stressed elongated configuration within thecatheter sheath 22. The operation to embed the tissue anchor 24 may becontrolled under visualization, such as by providing radiopaque markersin and around the tissue anchor 24 and distal end of the catheter sheath22, as will be explained.

The exemplary tissue anchor 24 is disclosed in U.S. Pat. No. 9,474,605,expressly incorporated herein, which also discloses other tissue anchorsthat may also benefit from the solutions described herein. U.S. Pat. No.8,932,348, also expressly incorporated herein, provides further detailsof tissue anchors similar to the tissue anchor 24. Tissue anchors thatinclude tines or barbs that pierce the tissue and elastically changeshape to hold onto the tissue especially benefit from the conceptsdisclosed herein. However, other tissue anchors that require a minimumamount of contact force in order to properly deploy may also be modifiedto include the various embodiments disclosed herein. Applicantstherefore emphasize that unless any particular claim enumerated belowspecifies the type of tissue anchor, all such “piercing” tissue anchorsare suitable candidates.

To facilitate central positioning of the anchor rail 26 duringdeployment the device is implanted with the assistance of an imagingsensor such as an ex vivo (outside the body) fluoroscope. For example,after properly positioning the patient so as to maximize the view of thetarget annulus, e.g., the tricuspid annulus, a pigtail catheter isplaced in the right ventricle and contrast injected. This allows theuser to see a clear outline of the annulus and the right ventricle. Atthis point, a frame of interest is selected (e.g., end systole) in whichthe annulus is clearly visible and the annulus to ventricular apexdistance is minimized. On the monitor, the outline of the rightventricle, the annulus, and the pulmonary artery are traced. The centerof the annulus is then identified and a reference line placed 90°thereto is drawn extending to the right ventricular wall. This providesa clear linear target for anchoring. In a preferred embodiment, theanchor 24 is preferably located in the base of the ventricle between theseptum and the free wall.

Aligning the anchor rail 26 in this manner helps center the eventualpositioning of a coapting element of the system within the tricuspidleaflets. If the coapting element is offset to the anterior or posteriorside, it may get stuck in the tricuspid valve commissures resulting inleakage in the center of the valve. An alternative method is to place adevice such as a Swan Ganz catheter through the right ventricle and intothe pulmonary artery to verify that the viewing plane is parallel to theanterior/posterior viewing plane. Addition of a septal/lateral view onthe fluoroscope may be important to center the anchor in patients thathave a dilated annulus and right ventricle. Further, the presence of theguide balloon 28 (FIG. 1A) centers the anchoring catheter 20 through theleaflets of the tricuspid valve TV and reduces large misalignments.

Various imaging sensors may be utilized to visualize the position andconfiguration of the tissue anchoring catheter 20 and surroundinganatomical structures. Fluoroscopy is essentially a continuous X-raybeam that can distinguish between various anatomical structures andsurgical instruments or materials within the body. Alternatives tofluoroscopy include ultrasound, optical imaging, magnetic resonanceimaging (MM), and the like. Some of these devices function exclusivelyfrom outside the body (ex vivo), while others may require an in vivoprobe. All have some type of display (e.g., video screen) that informsthe operator about the position and configuration of various objects inthe field of visualization. The term imaging sensor refers to thesensing transducer for any of these technologies and should not beconsidered limited to fluoroscopy, even though that is most commonlyused during cardiac surgery.

The present application contemplates several methods for ensuring thatthe proper pressure is applied by the tissue anchoring catheter againstthe tissue so the tissue anchor securely deploys. One method involvesvisualizing the distal end of the tissue anchoring catheter from outsidethe body using a display for an imaging sensor, where the distal end ofthe catheter changes configuration when it is pressed against thetissue. Another method involves automatically regulating the pressureapplied to the tissue prior to deployment of the tissue anchor, whichmay also be used in conjunction with visualization. Several safety locksto prevent deployment of the tissue anchor prior to establishment of theproper pressure are disclosed, which again may be used withvisualization and/or an automated pressure regulator. Indeed, a numberof separate technical aspects disclosed herein may be combined invarious ways, and the application should not be considered limited toany one particular illustrated embodiment. More specifically, it shouldbe understood that any illustrated embodiment shown and described hereincan be combined with any other illustrated embodiment as long as thetechnical aspects are not mutually exclusive or otherwise physicallyredundant.

Most notably, the pressure-regulating aspects of the devices and methodsfor ensuring accurate placement and secure deployment of a tissue anchorsuch as anchor 24 shown in FIGS. 1A-1C are suitable for use with ananchor by itself. That is, the techniques may be used to embed an anchor24 without connection to a tether such as the anchor rail 26. Indeed,one embodiment for deploying tissue anchors by themselves is describedbelow with reference to FIGS. 21-24. Accordingly, any and all of thesubsequently described devices and methods may be combined in a systemsimilar to that shown in FIGS. 21-24 that deploys tissue anchors bythemselves, absent a tether.

Visualization of the Tip of the Tissue Anchoring Catheter

A first technique to ensure proper pressure is applied by the catheteragainst the tissue involves visualization by an imaging sensor. FIG. 2Ais an exploded view of a tissue anchor 24 (shown partly in section) andrail 26 along with an assembly of components 50 on the distal end of theanchoring catheter 20 for regulating the pressure of the catheteragainst tissue including an internal spring member, and FIG. 2B is anassembled view of the pressure regulating assembly 50. It should benoted that the tines 30 of the tissue anchor 24 are shown flexed intoelongated shapes for passage through the anchoring catheter 24, and alsoshown in dashed line 30′ in their relaxed configuration curled back uponthemselves which occurs upon ejection from the catheter and deploymentinto tissue. Also, the anchor rail 26 is cut short for clarity, and maybe many feet long. The assembly 50 includes a distal tubular housing 52that slides axially within a tubular housing frame 54 that is surroundedby a thin tubular cover 56. A distal end of an elongated pusher 60engages via a coil spring 62 a proximal end of the housing frame 54. Thecoil spring 62 is centered on a short radially recessed portion 63 ofthe pusher 60 and extends between the pusher and a proximal end of thetubular housing 52. The distal end of the pusher 60 may be fixed withrespect to the housing frame 54, as well as to the proximal end of thecoil spring 62.

The tubular housing 52 includes an enlarged distal tip 64 formed as athick echogenic ring, such as by providing changes in diameter, chamfersor knurling on an exterior periphery thereof, as shown. (In thiscontext, “echogenic” does not strictly refer to the sound reflectiveproperties of the distal tip 64, but to its ability to effectivelyreflect various types of waves, such as the X-rays used in fluoroscopy.)The tip 64 preferably has a chamfered front outer corner which also aidsin preventing tissue from getting caught on the tip. The majority of thetubular housing 52 has a much thinner wall thickness than the relativelylarge mass distal tip 64 and terminates at its proximal end in aplurality of axial slots that form a pair of diametrically-opposedcantilevered sections 66 each having an outwardly-directed retention tab68. The exterior diameter of the proximal end of the tubular housing 52fits closely within the lumen of the housing frame 54, and eachretention tab 68 has a proximal ramp that permits the cantileveredsections 66 to flex inward upon insertion of the tubular housing 52 intothe distal end of the housing frame 54. Rotational alignment of thetubular housing 52 within the housing frame 54 enables the retentiontabs 68 to snap outward into axial slots 70.

As seen in FIG. 2B, the tubular cover 56 may be adhered or welded to theoutside of housing frame 54 and conceals the slots 70. Because thedistal end of each of the retention tabs 68 has a radial face, thetubular housing 52 is retained within the housing frame 54 and can slideaxially therein between distal and proximal positions.

FIGS. 3A-3D are sectional views of steps in positioning the exemplarytissue anchoring catheter having the distal assembly 50 of componentsover a target tissue site T. It should be noted that for clarity thesefigures do not show an outer flex shaft or sheath such as shown at 22 inFIG. 1A (e.g., Pebax material) that surrounds the assembly 50, nor theguide balloon 28 mentioned above which would be incorporated into theouter shaft.

In use, the operator negotiates the catheter 20 through the body intoproximity to the tissue target T, as explained above in the context ofdeploying a cardiac anchor. The coil spring 62 biases the distal tubularhousing 52 distally so that the distal tip 64 projects from within thehousing frame 54. Engagement of the tabs 68 on the tubular housing 52with the distal extent of the axial slots 70 in the housing frame 54retains the housing within the frame. It will be understood, however,that the tubular housing 52 may be displaced proximally into the housingframe 54 against the spring 62, at least to the compressive limit of thespring or when the housing contacts some other physical impediment.

FIG. 3B illustrates the distal advancement of the entire distal catheterassembly 50 until the distal tip 64 contacts the tissue surface tissuesurface. As mentioned above, this position of the catheter prior todeployment of the tissue anchor 24 is typically accomplished undervisualization.

FIG. 3B also illustrates an internal annular ridge 72 formed on aproximal end of the tubular housing 52. The ridge 72 interferes with atapered hub 74 that forms a part of the tissue anchor 24. In particular,the hub 74 fastens around the anchor rail 26 and the tines 30 aresecured to the hub. The interference between the inner ridge 72 andtissue anchor hub 74 provides a stop that prevents the tissue anchor 24from being pulled out of the tubular housing 52 and into the middle ofthe spring 62. Engagement between the ridge 72 and hub 74 is anotherimpediment that prevents the moving housing 72 from ever becomingdetached completely from the catheter, as it is always retained thereonby the tissue anchor 24.

Once in the position of FIG. 3B, the operator determines whether thedistal tip 64 is centered over the tissue target T. In the meantime, theoperator may further advance the catheter 50 and connected housing frame54 to compress the spring 62, as seen in FIGS. 3C and 3D. Although notshown, the pusher 60 preferably extends back to a proximal handle and anactuator which slides it forward and backwards, or is coupled to asecondary shaft (not shown) which extends proximally to the handle. Itshould be understood that there are various ways for axially displacingthe pusher 60. At the point where the spring 62 is fully compressed (orleast compressed to a desired amount), a distal portion of the housingframe 54 comes into close proximity with the thick distal tip 64 of thetubular housing 52. It should be noted that the thicker distal tip 64 isless traumatic to tissue against which it is pressed.

A schematic image of the appearance of the distal assembly of components50 in this sequence is seen in FIGS. 10A and 10B, wherein the relativelythick housing frame 54 shows up as a dark rectangular mass thateventually moves into close proximity with the relatively large massdistal tip 64 that also shows up as dark on the image display. Theremainder of the tubular components have lesser wall thicknesses, and incontrast show up less distinctly on the image display. The operator canthus tell when the spring 62 has been fully compressed (or leastcompressed to the requisite amount). However, upon further examinationof the image display from the position of the components relative to theanatomy in FIG. 3D, the operator may conclude that the catheter is notcentered over the tissue target T, and thus will not deploy the tissueanchor 24.

FIG. 4A illustrates a step of repositioning the tissue anchoringcatheter by first retracted proximally the pusher 60 and housing frame54. This relaxes the spring 62 and separates the distal end of thehousing frame 54 from the distal ring 64. FIG. 4B shows lateraldisplacement of the catheter until it is centered over the tissue targetT, at which point it is once again advanced until the distal tip 64 isin contact with the tissue wall, as in FIG. 4C. Subsequently, thecatheter pusher 60 is once again displaced distally to advance thehousing frame 54 relative to the tubular housing 52.

In FIG. 4D, the thick distal end of the housing frame 54 has once againreached the echogenic distal tip 64, which convergence shows up clearlyon the external imaging display (see, e.g., FIG. 10B) thus notifying theoperator that the desired compressive force for anchor deployment hasbeen reached. Several alternative configurations of a distal assembly ofcomponents on the catheter which affords good visibility using animaging sensor/display are disclosed herein, some of which are discussedbelow with regards to FIGS. 11 and 12.

As mentioned above, the coil spring 62 may be completely compressed, asshown, though this is not strictly necessary and the spring may be onlypartly compressed. In either case, compression of the spring 62 at themoment when the distal end of the housing frame 54 reaches the distaltip 64 provides a calibrated and desirable compressive force of thecatheter against the tissue. That is, the spring constant is calibratedso that linear compression to the extent seen in FIG. 4D produces acontact force which will ensure that the tissue anchor 24 will properlyembed within the tissue once advanced from the tubular housing 52. Aswill be understood, the particular contact force for which the spring 62is calibrated depends on a number of factors such as the size andconfiguration of the tissue anchor 24, the character of the tissue intowhich anchor is embedded, and the subsequent forces expected to beimparted to the anchor rail 26 once fully implanted, among others. In anexemplary embodiment, the illustrated tissue anchor 24 is properlyanchored within the ventricular tissue when expelled from the catheterthat exerts a contact force against the tissue of between 0.5-2.0 N, andmore preferably about 1.0 N.

Subsequently, as seen in FIG. 4E, the operator separately advances theanchor rail 26 through a lumen in the pusher 60. Although not shown,further advancement of the tissue anchor 24 causes it to be embeddedwithin the tissue. Because of the compressive force imparted by thecatheter 20 on the tissue, an equal and opposite reactive force from thetissue is established. The tissue anchor 24 encounters this force uponemerging from the distal tip 64, and consequently deploys in theexpected manner.

It should be noted that the “anchor rail 26” is shown as a hollowflexible tube, but may be a braided cable to the end of which attachesthe tissue anchor 24. In that case, a thin-walled tubular pusher may beused over the cable that engages the tissue anchor 24. A tubular pusher26′ is actually shown in FIG. 4E. It should also be noted that theanchor rail 26 has sufficient linear compressive strength to advance thetissue anchor 24, and thus functions as a pusher in itself. In thisregard, the anchor rail 26 acts as an anchor tool to advance the tissueanchor 24. As mentioned above, the anchor 24 may be installed by itselfwithout the anchor rail 26, such as for instance if the two componentsare detachable, in which case the anchor rail 26 functions simply as apusher tool and not as a subsequent tether for the anchor 24.

Automated Deployment of the Tissue Anchor and Deployment Locks

The tissue anchor catheter 20 described above requires advancement of aportion of the catheter to establish a proper compressive force againstthe target tissue followed by a separate or autonomous advancement ofthe tissue anchor rail. However, these functions may be combined into asingle movement. That is, the same element that creates the compressiveforce may also advance the tissue anchor in a so-called “push-to-fire”configuration. As will be seen, this configuration of tissue anchorcatheter may be utilized with or without simultaneous visualization ofthe distal tip. That is, if the compressive force is actuatedautomatically by advancing the catheter into the tissue wall, there maybe no need to ensure proper force regulation by external imaging. On theother hand, adding visualization provides redundancy in the system, andas will be explained below, may actually be necessary for properoperation.

FIG. 5 illustrates an exploded assembly of components 80 for a distalend of a tissue anchor catheter that combines the force generationfunction with the tissue anchor advancement function in one action. Theassembly 80 includes a distal tubular housing 82 again having a ring 84on a distal end with a wide echogenic outer surface and chamferedforward corner that contacts the tissue wall. The proximal portion ofthe tubular housing 82 has a thin wall for fluoroscopic contrast withthe ring 84, and features a pair of longitudinal slits that create atleast one cantilevered finger 86 with an outwardly-projecting retentiontab 88 on a proximal end thereof. Preferably there are a number of suchcantilevered fingers 86 and tabs 88 around the circumference of thetubular housing 82 intermediate cantilevered sections of the tubularhousing.

As seen in FIGS. 6A and 6B, the tissue anchor 24 on the distal end ofthe anchor rail 26 resides within the hollow tubular housing 82. Thetubular housing 82 slides within a push-to-fire tubular frame 90 whichhas a longitudinal slot 92 cut into at least one side to interact withretention tabs 88 on the housing 82, as will be explained. The frame 90has an outer tubular cover 94 which extends over the longitudinal slot92, and also closely houses a coil spring 98. A lockout wire 96 extendsthrough the longitudinal slot 92, and a pull wire 97 may be provided forsteering the distal end of the catheter.

A generally tubular pusher 100 has a distal portion 102 that extendsclosely within the coil spring 98 and an enlarged proximal end thatforms an annular shoulder 104 with the distal portion 102. A small step106 at the distal end of the distal portion 102 provides a space withinwhich the retention tab 88 may be biased, as will be explained.

FIGS. 6A and 6B are sectional views of the alternative pressureregulating assembly 80 showing removal of a lock that preventsadvancement of the tissue anchor 24. It should be noted that the tubularframe 90 and pusher 100 may be adhered or welded to each other so as tomove together, and the pull wire 97 is desirably welded to a proximalend of the pusher 100 on one side thereof. When the operator pulls thewire 97 such as from a proximal handle (not shown), the device bends orarcs in the same plane as the pull wire. Rotating the catheter about itsaxis enables steering in 360°. As mentioned above, although thissteering mechanism is only shown in the embodiment of FIGS. 6A-6B, itmay be incorporated into any other of the tissue anchoring catheterversions disclosed herein.

FIG. 6A shows the lockout wire 96 extended through the longitudinal slot92 in the frame 92 to an approximate midpoint of the tubular housing 82.The wire 96 contacts the outwardly-directed retention tab 88, and thusbiases it inward into engagement with the distal step 106 on the forwardend of the pusher 100. Preferably, the retention tab 88 has a rampedouter proximal edge such that the lockout wire 96 may be easily insertedduring assembly in a distal direction through the slot 92 and to cam theretention tab 88 inward. Because the retention tab 88 has a radialcorner at the proximal end of the step 106, it prevents distal movementof the pusher 100 relative to the tubular housing 82. Furthermore,displacement of the pusher 100 is the sole means of advancing the tissueanchor 24 through the tubular housing 82 by virtue of engagement betweena distal face of the pusher 100 and the tapered hub 74 of the tissueanchor 24. Consequently, the retention tab 88 prevents advancement ofthe tissue anchor 24 from within the tubular housing 82.

Once the catheter has been maneuvered such that the distal tip 84 is incontact with the target tissue, as can be verified with externalvisualization, the lock 96 may be released to enable advancement of thetissue anchor 24. FIG. 6B shows proximal retraction of the lockout wire96, typically actuated from a proximal handle (not shown). This freesthe retention tab 88 to flex outward as seen, out of engagement with thedistal step 106 on the pusher 100. This in turn frees the pusher 100 tobe displaced in a distal direction relative to the tubular housing 82.

Subsequently, forward or distal movement of the pusher 100 compressesthe spring 98 between the shoulder 104 of the pusher 100 and the tubularhousing 82. Although not shown, the pusher 100 compresses the spring 98to a desired amount at the moment that the tissue anchor 24 reaches theopen distal mouth of the tubular housing 82. Further advancement of thepusher 100 drives the tissue anchor 24 into the tissue, again with thedesired amount of compressive force applied to the tissue. Thisconfiguration thus provides an automatic force regulation and tissueanchor deployment, coupled with a safety feature which preventspremature movement of the tissue anchor.

FIGS. 7A and 7B are schematic views of alternative locks that can beused to prevent premature movement of the tissue anchor. In FIG. 7A, alockout wire 110 extends forward into engagement with a lockout ball 112mounted to slide in and out of a channel formed within the housing frame90 and forces the ball radially inward into a groove (not numbered) onthe outside of the tubular housing 82. Since the housing frame 90 andpusher 100 are coupled together, the tubular housing 82 can be preventedfrom moving relative to the pusher 100 in the position shown. Retractionof the lockout wire 110 permits the lockout ball 112 to move outwardinto the channel in the frame 90, which permits relative movement of thetubular housing 82. Thus, the pusher 100 can move forward relative tothe tubular housing 82 and eject the tissue anchor 24.

In FIG. 7B, a lock assembly includes a pull wire 114 that extends fromproximal handle into an elongated opening 116 in the tubular frame 90.The pull wire 114 connects with a movable wedge member 118 thatinteracts with an outward tab 119 on the housing 82. By virtue of theshape of the opening 116, the wedge member 118 prevents movement of thetab 119, and thus locks the tubular housing 82 with respect to thehousing frame 90. Retraction of the pull wire 114 disengages the wedgemember 118 from the tab 119, thus permitting movement of the tubularhousing 82 relative to the housing frame 90. Furthermore, numerous otherlocking mechanisms are contemplated.

FIGS. 8A-8D are sectional views of steps in positioning a furtheralternative tissue anchoring catheter over a target tissue site T. Theassembly of components on the distal end of the catheter is similar tothe assembly described above the respect to FIGS. 6A-6B except without asafety lock to prevent premature movement of the tissue anchor.Therefore, like elements will be given like numbers. In particular, apusher 100 has a distal portion 102 that extends through the coil spring98 and abuts a proximal end of the hub 74 of the tissue anchor 24.Displacement of the pusher 100 therefore also displaces the tissueanchor 24. Furthermore, the housing frame 90 is configured with arelatively thick radiopaque distal portion 120 that is used forvisualization in conjunction with the thick distal ring 84 on thetubular housing 82. This configuration is thus a combination or hybridof the distal assembly of components described with regard to FIGS. 3-4having moving components that are easily visible using an imagingsensor/display, with the assembly of FIGS. 6A-6B wherein the tissueanchor 24 can be automatically deployed by simply displacing the pusher100 in a distal direction. FIGS. 8A-8D shows several steps in advancingthe catheter into contact with the tissue then repositioning thecatheter until it is in alignment with the target site T.

FIGS. 9A and 9B illustrate steps of deploying the hybrid tissue anchorof FIGS. 8A-8D into the tissue using a pressure regulating assemblyhaving an automatic deployment arrangement as well as visibleindicators. Once the target site T is reached, the operator advances thepusher 100 which advances both the tissue anchor 24 as well as the thickdistal portion 120 on the housing frame 90. In FIG. 9B, the tines 30 ofthe tissue anchor 24 have reached the tissue surface, whereas the spring98 is not fully compressed. This position of the tissue anchor 24 alsocorresponds to abutment of the radiopaque distal portion 120 of thehousing frame 90 with the thick distal ring 84, which can easily be seenon an external display. At this point, the force applied to the tissueis calibrated such that further advancement of the tissue anchor 24properly deploys it at the target site T. Such further advancement isdone by distal movement of the pusher 100, until the spring 98 is fullycompressed, in the automated “push-to-fire” configuration.

In an alternative embodiment, FIG. 9C shows the assembly with the tissueanchor 24 against the tissue surface, but with the spring 98 alreadyfully compressed. In this configuration, further advancement of thepusher 100 is undesirable because it would just excessively press theentire assembly against the tissue and not eject the tissue anchor 24.Instead, advancement of the tissue anchor 24 is accomplished viaseparate advancement of the anchor rail 26, as described above.Consequently, this arrangement is not a fully automated anchoringmethod, even though the pusher 100 delivers the tissue anchor 24 to thetissue surface, and requires a separate movement of the anchor rail 26.

Visualization Alternatives

FIGS. 10A-10B are schematic views of the distal end of a tissueanchoring catheter of the present application showing differentfluoroscopic images visible using an external imaging sensor of twopositions of the pressure regulating assembly. The schematic views maycorrespond to several embodiments described above, such as the distalassembly 50 having a relatively movable tubular housing 52 relative tothe housing frame 54. Upon contact of the thick distal ring 64 againsttissue and further advancement of the frame 54, the thick-wall housingframe 54 shows up dark on the image display clearly abutting the darkdistal ring 64. This signifies that the proper compressive force hasbeen established between the catheter and the tissue, and that thetissue anchor and can be deployed.

FIGS. 11A-11C are schematic views of fluoroscopic images visible on anexternal imaging sensor/display of an alternative pressure regulatingassembly in different positions. In this instance, a movable sleeve thatmay form a part of the housing frame 54 includes a radiopaque band 132on a distal end thereof. A tubular housing 52 that contacts the tissuemay have a smaller radiopaque band 134 located at a mid-portion thereof.Advancement of the housing frame 54 as seen in FIG. 11B eventuallyaligns the radiopaque bands 132, 134, which signifies that propercompressive force has been established. FIG. 11C illustrates furtheradvancement of the housing frame 54 which displaces the largerradiopaque band 132 distally passed the smaller band 134. This“overshoot” may signify that excessive force has been applied to thetissue, thus informing the operator to back off the housing frame 54.

FIGS. 12A-12B are schematic views of fluoroscopic images visible on anexternal imaging sensor generated by a further alternative pressureregulating assembly. In this embodiment, an element such as the housingframe 54 described above may be provided with a series ofcircumferential radiopaque bands 140 that show up dark underfluoroscopy. Likewise, the tubular housing 52 defines a series ofsmaller circumferential radiopaque bands 142 that also show up as darkrings. Upon distal displacement of the tubular housing 52, the bands140, 142 line up as in FIG. 12B, thus exhibiting an alternating dark andlight pattern. This signifies to the operator that the propercompressive force has been reached. Additionally, numerous otherradiopaque marker configurations are contemplated, and the embodimentsdisclosed should not be considered limiting.

In addition to providing visual indicators on the distal end of thecatheter which can be monitored to determine when the proper force isapplied to the tissue, other signals such as audio or tactile feedbackmay be used. For example, the various springs incorporated in thecatheters disclosed herein may be replaced or supplemented by a straingauge or piezo-electric sensor which transmits an electric current tothe proximal end of the catheter upon being subjected to compressiveforce from contact with the tissue. The current can then be used tocontrol an audio output, such as a tone with a gradually increasingvolume or a series of tones which increase in frequency the closer tothe desired compressive force. The current could also be used toeliminate a signal light when the proper compressive force is reached.Those of skill in the art will understand that these and various otherindicators may substitute for or supplement the visual indicatorsdisclosed herein.

Yet another solution is to incorporate a clutch mechanism of some sortat the distal tip of the catheter such that the operator can applycompressive force only up to the desired value after which the clutchmechanism slips and provides a tactile feedback to the operator. Aclutch arrangement such as this provides a fail-safe pressure regulatingmechanism.

FIGS. 13A and 13B are perspective views of distal ends of tissueanchoring catheters showing alternative echogenic tips for high externalvisibility. In FIG. 13A, an echogenic distal tip 150 is provided at thedistal end of a tubular housing 152, which may be the same as thetubular housing 52 described above with respect to FIGS. 2-3. Tubularhousing 152 slides within a tubular housing frame 154, which again maybe the same as housing frame 54. The frame 154 preferably has aradiopaque band 156 on a distal end thereof which shows up on anexternal imaging sensor/display relative to the echogenic distal tip150. The distal tip 150 is shown having a knurled exterior whichprovides a plurality of crisscrossed reflective surfaces to increaseradiopacity. A generally cylindrical guide balloon 158 having taperedends 160 is shown mounted around the outside of the catheter.

FIG. 13B illustrates a similar structure with an echogenic distal tip150′ on the distal end of the tubular housing 152′. Again, a tubularframe 154′ within which the housing 152′ slides preferably has aradiopaque band 156′ on a distal end thereof which shows up on anexternal imaging sensor/display relative to the echogenic distal tip150′. In this embodiment, the tip 150′ presents a series of roundrecesses or dimples 162′ (which could also be formed as protrusions)that enhance the reflective nature of the tip. Of course, many otherstructures which improve the reflectivity of the catheter tips arecontemplated, and the same structures can be added to the reflectivebands 156, 156′ on the housing frames, or any other surface whichfunctions as a visibility indicator.

Spring Alternatives

FIGS. 14A-14C are elevational views of alternative springs that may beused in the tissue anchor catheter pressure regulating assemblies inplace of the internal coil springs disclosed above, such as that shownat 62 in FIG. 2. For instance, FIG. 14A illustrates an assembly ofcomponents at the distal end of a catheter 170 having an external springmember 172 formed from a tubular member 174 with a collapsible patterncut into it, such as by using a laser. The tubular member 174 is made ofa radiopaque material so as to be visible under fluoroscopy. A proximalend 175 of the tubular member 174 would be fixed to a shaft 176extending from a distal end of a guide balloon 177. Although not shown,a movable tissue anchor is housed within the shaft 176. A distal end ofthe spring member 172 preferably has an enlarged ring 178 thereon whichhas enhanced visibility under fluoroscopy, or other such imagingtechnology. The enlarged ring 178 extends beyond a distal end of theshaft 176 so as to form a leading end of the catheter 170. When thecatheter 170 is pressed against a tissue surface, the tissue exerts aproximal reaction force against the distal ring 178 which at apredetermined magnitude causes the spring member 172 to collapse. Therelative proximal movement of the distal ring 178 and collapse of thespring member 172 shows up on the external sensor/monitor to notify theoperator that a desired compressive force has been reached. As before,the structure of the spring member 172 is calibrated to collapse at adesired compressive force.

FIG. 14B shows an assembly of components at the distal end of a catheter180 having an external spring member 182 welded between two externalmetal rings 184, 186. A distal ring 184 is highly visible underfluoroscopy and may have a radially wide distal flange 188 to broadenthe tissue engagement surface and reduce the possibility of damagethereto. The distal ring 184 is desirably fixed around a tubular housing190 that slides within a larger tubular housing frame 192 to which theproximal ring 186 is fastened. Advancement of the catheter 180 againstthe tissue surface thus displaces the tubular housing 190 in a proximaldirection into the housing frame 192 against the bias of the spring 182.Again, the spacing between the two metal rings 184, 186 shows up clearlyon fluoroscopy and can be used to determine when the proper compressiveforce is reached.

Finally, FIG. 14C illustrates an assembly 200 in which a compressivespring is formed by a spiral cut pattern 202 in a tubular member 204.The tubular member 204 extends between two radiopaque markers 206 whichcome together after the catheter 200 is pressed against tissue and thespring collapses.

Combined Spring and Visualization

FIGS. 15A-15E are sectional views of still further alternative springsformed by flexible plunger-like structures on the distal or leading endof the tissue anchor catheter that deform upon contact with tissue, andmay also act as visual indicators such as being made from radiopaquematerial. As demonstrated by the alternative springs shown in FIGS.14A-14C, there are a number of ways to establish a predeterminedcompressive force against the tissue into which the anchor is embedded.The present application contemplates internal and external coil springsformed as separate elements, springs that are cut into catheter tubing,elastomeric sleeves or other such compressible elements, as well as theplunger-like structures of FIGS. 15A-15E.

FIG. 15A shows a distal end of a tissue anchor catheter 210 having alumen through which a tissue anchor 212 travels. A flexible plunger-likedistal tip 214 attaches to the distal end of the catheter tube andextends beyond the tube so as to form the leading end. The distal tip214 is desirably an elastomer having radiopaque properties, such assilicone with barium sulfate particles embedded therein. The distal tip214 in its relaxed configuration as shown has a tubular collar 216secured around the catheter 210 and a half-doughnut shaped flap 218extending distally from the catheter and curving outward and backapproximate 180°. Preferably, a portion of the catheter 210 adjacent thedistal tip 214 is also radiopaque. When the catheter 210 is pressedagainst tissue, the flap 218 deforms in a proximal direction whichmovement relative to the catheter can be seen on a fluoroscope.

FIG. 15B illustrates an alternative plunger-like distal tip 220 which isalso preferably elastomeric and radiopaque. The tip 220 has a proximalportion attached to the catheter and a distal portion in the shape of aforward-facing cup that forms a leading end of the catheter. Again,pressure against the tissue wall deforms the tip 220 which is seen on anexternal imager/display. An elastomeric/radiopaque distal tip 222 shownin FIG. 15C is formed in the shape of a trumpet horn such that pressureagainst a tissue wall causes the tip to flare outward in a proximaldirection. The elastomeric tip shown in FIG. 15D is somewhat similar tothe tip 214 of FIG. 15A but also includes a radiopaque ring 224 embeddedaround a proximal edge. Movement of the radiopaque ring 224 shows upreadily on the external imager display. Finally, FIG. 15E shows a softor flexible annular tip 226 disposed on and forming a leading end of thecatheter which is biased in a distal direction by a coil spring 228. Thetip 226 may not deform to the extent of the previously-describedplunger-like tips, but is radiopaque and may be pushed backward uponcontact with the tissue surface against the bias of the spring 228.Movement of the tip 226 thus indicates the level of force applied by thecatheter against the tissue. Desirably, the tip 226 has a front facethat has rounded surfaces and corners, such as the trumpet-like shapeshown.

FIGS. 16A-16C illustrate a still further alternative pressure regulatingassembly for the tissue anchor catheters of the present application. Ina tissue anchoring catheter 250, an exterior expandable braided tube 252typically made of Nitinol attaches at a distal end 253 around an innershaft 254, and at a proximal end 255 around an outer shaft 256. Thebraided tube 252 can be converted from a relatively narrow deliveryconfiguration seen in FIG. 16A to an expanded configuration seen in FIG.16B by proximally displacing the inner shaft 254 relative to the outershaft 256. This displacement of the inner shaft 254 can be a result ofcontacting the distal end 253 against tissue just prior to deploying ananchor (not shown). The braided tube 252 possesses an elasticity thatrequires a particular force to compress it to the expandedconfiguration, which force can be calibrated to correspond to a desiredcompressive force against the tissue. Expansion of the braided tube 252can be detected through various means as described herein, includingsimply forming the tube from a radiopaque material such as Nitinol orproviding radiopaque markers thereon and monitoring its shape.Alternatively, the ring-shaped distal end 253 and proximal end 254 maybe radiopaque such that the operator can monitor their relative axialspacing via an external imager as an indicator for when the braided tube252 expands and shortens axially.

FIG. 16C illustrates a prototype of the expandable braided Nitinol orpolymer mesh tube 252 at the distal end of the catheter 250. In additionto providing the pressure regulating function for the tissue anchor asdescribed herein, the braided tube 252 can substitute for the guideballoon used to assist in advancing the anchoring catheter to the targetlocation. Conventional guide balloons, such as the guide balloon 28shown in FIGS. 1A-1B, are inflatable polymeric structures that must beleak tested prior to use. Substitution of the expandable braided tube252 eliminates the possibility of leaks and thus is more reliable andfacilitates manufacture by obviating any leak testing. The braided tube252 can be converted to its expanded configuration by providing controlof the inner shaft 254 relative to the outer shaft 256 from a proximalhandle (not shown).

FIGS. 17A and 17B illustrate an alternative pressure regulating assemblyincluding an internal bellows-like structure 260 in two differentpositions, and FIG. 17C shows an internal spring that may incorporateradiopaque markers. The bellows-like structure 260 may be constructedfrom a segment of different tube as in FIGS. 17A and 17B, or as seen incross-section in FIG. 17C as a thin section in an elongated cathetershaft 262. The bellows-like structure 260 bows outward when the shaft262 is compressed against the tissue, as seen in FIG. 17B. An internalspring 264 shown in in FIG. 17C may be situated in the recessed areacreated by the thin-walled structure 260 and provides resiliency andspring back to straighten the catheter shaft 262 when compression ends.The spring 264 may also be radiopaque or have markers thereon to enhancethe visualization of the compressed catheter. A guide balloon 266 isshown surrounding the distal end of the catheter 262, and may be bulbousin shape as in FIGS. 17A and 17B, or more cylindrical as in FIG. 17C.

Preliminary Tip Retraction

A number of the pressure regulators described herein rely on aspring-biased distal end of the catheter shaft which retracts into themain portion of the catheter when pushed against tissue. These devicestend to elongate the distal end of the device beyond the guide balloon,which is not desirable because the distal tip can become entangled withanatomical structures or cause damage if inadvertently maneuvered intodelicate tissues. Consequently, the present application contemplatesseveral solutions described below.

FIG. 18A is a schematic view of the distal end of an exemplary tissueanchor catheter 300 of the present application showing extension ofspring-loaded tip 302. FIG. 18B is a schematic view of a preferredretracted position of the spring-loaded tip 302 during delivery. A guideballoon 304 is shown on the exterior of the catheter 300. The extensionof the tip 302 beyond the balloon 304 as in FIG. 18A is preferablyminimized by retracting or “choking up” on the tip 302 to the positionof FIG. 18B.

FIGS. 19A and 19B are schematic views of two different solutions forenabling retraction of the spring-loaded tip 302 as in FIG. 18B. In theexample of FIG. 19A, a tissue anchor 306 is shown held within thetubular tip 302 with an anchor rail 308 extending proximally therefrom.A spring 310 that can also be used for the force regulation, or may be asecondary spring, is located within the catheter tube 300 just proximalto the tip 302. By virtue of stops 312 within the spring-loaded tip 302,the tip can be retracted by pulling in a proximal direction on theanchor rail 308. In one embodiment, the anchor rail 308 may be retractedusing a control on a proximal handle (not shown) and held in theretracted position. This retracts or “chokes up” the tip 302 duringdelivery of the catheter 300 to reduce the extent of the catheter beyondthe external guide balloon (not shown in FIG. 19A). Once the distal endof the catheter is maneuvered into position adjacent the tissue targetsite, the anchor rail 308 is released to extend the spring-loaded tip302, and the aforementioned force regulation step can be performed.

FIG. 19B illustrates one exemplary tissue anchoring catheter having aproximal handle 320, a pusher shaft 322, an anchor rail tensioner 324,and an anchor rail 326 which extends to a distal end of the catheter(not shown). A proximal end of the anchor rail 326 fastens to a carriage328 arranged for sliding movement within the rail tensioner 324. Thecarriage 328 is biased by a spring 330 within the rail tensioner 324 ina proximal direction. In this manner, the anchor rail 326 is biased in aproximal direction, which pulls the distal tip 302 into the cathetertube by virtue of its interaction with the tissue anchor therein(similar to anchor 306 in FIG. 19A). After the catheter is maneuveredinto position adjacent the tissue target site, the operator advances thepusher shaft 322 which extends the distal tip 302. After contact withtissue, the rail spring 330 pulls the distal tip 302 back into thecatheter shaft against the bias of a force regulation spring (not shown)as described above.

FIGS. 20A and 20B show one arrangement for a guide balloon 350 attachedto the exterior of the distal end of a tissue anchor catheter 352 toreduce the extent of the catheter that projects distally from theballoon. The shaft of the catheter has an enlarged proximal portion 354,such as by virtue of placing a tubular spacer 356 therein. The shaft 354reduces in diameter at step 358 to a narrower distal portion 360. Aproximal collar 362 of the balloon 350 attaches to the larger proximalportion 354, while a distal collar 364 attaches to the smaller distalportion 360 after having been inverted. That is, the balloon 350 has anexterior surface 366 and an interior surface 368. The proximal collar362 is formed by adhering the interior surface 368 to the outside of thecatheter shaft, while the distal collar 364 is formed by inverting theballoon material and adhering the exterior surface 360 to the outside ofthe catheter shaft. This method of construction causes the balloon 350to have an enlarged or bulged distal end which effectively reduces thelength of the catheter 352 that projects distally therefrom. This helpsprevent contact of the distal tip of the catheter with cardiac tissuewhich can cause damage thereto.

The techniques described herein for successfully installing anchors intissue by regulating the pressure applied by an installation tool are ofcourse transferrable to implant systems other than the ones describedabove. Indeed, unless limited by any one claim, the devices and methodsdisclosed herein are applicable to any surgical or minimally-invasiveanchoring solution. The example above of anchoring a tissue anchor 24 onthe distal end of a tissue anchor rail 26 for use in a coaptation systemfor reducing regurgitation through a native valve is particularlysalient as the motion of the ventricle in which the anchor is placedcreates issues for successful anchoring. However, other locations in thebody which undergo movement are good candidates for the anchoringtechniques. Below is a discussion of one such usage, implanting anannuloplasty ring with a plurality of anchors, though it will beunderstood that this represents just one of many potential applications,and the target location need not even be one that experiencespost-implant motion. Indeed, the type of anchor or the character of thetissue into which the anchors are placed may also be a factor thataffects whether the techniques described herein are beneficial.

FIG. 21A is a perspective view of a partial implant of an annuloplastyring 400 around a mitral annulus using the techniques described herein,and FIG. 21B shows the annuloplasty ring fully implanted. The particularannuloplasty ring 400 and deployment procedure are similar to thosedisclosed in U.S. Pat. No. 9,119,719 to Zipory, the contents of whichare expressly incorporated herein by reference. A commercial version ofsuch an annuloplasty ring 400 that utilizes the same deploymentprocedure is sold under the trade name Cardioband Mitral System byEdwards Lifesciences Corp. of Irvine, Calif. It should be noted that thedevices described in the following paragraphs may equally be used totreat the tricuspid valve or generally any of the heart valves.

The annuloplasty ring 400 is an open ring with two free ends 402, 404and a middle portion 406 that, when fully implanted, extends roughly270° around the mitral annulus, or generally around the posterior aspectto the annulus trigones. The annuloplasty ring 400 is installed througha sheath or catheter 410 which allows deployment through the patient'svasculature with the heart beating to reduce trauma to the patient. Asset forth in U.S. Pat. No. 9,119,719, a first free end 402 is firstexpelled from the catheter 410 and anchored to the annulus. Sequentialsegments of the flexible annuloplasty ring 400 are then anchored,one-by-one, as the rest of the ring is expelled from the catheter 410. Acontrol wire 412 that extends the length of the catheter 410 attaches tothe first free end 402 of the ring and is used to create the forcesneeded to feed the ring around the annulus and gradually expel it fromwithin the catheter. In the illustrated embodiment, the annuloplastyring 400 has a series of marker bands 414 along its length thatdelineate the segments of the ring, each of which is fastened by atissue anchor (not shown).

FIG. 22 shows one exemplary tool 420 for installing a tissue anchor thatcan be used to implant the annuloplasty ring as seen in FIGS. 21A and21B. The tool 420 comprises a proximal handle 422 having an elongatedflexible shaft 424 connected thereto and extending distally to an anchordriver 426. A corkscrew-like tissue anchor 428 is shown held by theanchor driver 426. The handle 422 preferably includes a pair of opposedtabs 430 that, along with the shaft 424, enable a user to apply torqueto the anchor driver 426 and thereby screw the tissue anchor 428 intotissue. The opposed tabs 430 may also be mounted for pivoting or axialmovement relative to the handle 422 to actuate a release mechanism (notshown) that decuples the tissue anchor 428 from the anchor driver 426.

FIGS. 23A and 23B are sectional views of an annuloplasty ring 400 beingimplanted. The tool 420 of FIG. 22 is used to install a plurality oftissue anchors 428 through a side wall of the ring 400 and into tissue.More particularly, the tool 420 with a tissue anchor 428 thereon ispassed through a flexible anchor catheter 440 of the present applicationthat extends through a hollow interior of the sleeve-like annuloplastyring 400. As explained in U.S. Pat. No. 9,119,719, a plurality ofanchors 428 are applied using the tool 420 by loading a first one of theanchors onto the anchor driver 426, and deploying the anchor into thecardiac tissue. The tool 420 may then be withdrawn from the subject'sbody (typically while leaving anchor catheter 440 in place in theannuloplasty ring 400), and a second one of the anchors 428 is loadedonto the anchor driver 426. The tool 420 is then reintroduced into theanchor catheter 440, and the second anchor is deployed. These steps arerepeated until all of the anchors 428 have been deployed. Alternatively,the entire deployment tool 420, including the anchor catheter 440, maybe removed from the body and subsequently reintroduced after beingprovided with another anchor 428. In a further alternative, the tool 420is configured to simultaneously hold a plurality of anchors 428, and todeploy them one at a time (configuration not shown).

FIGS. 24A-24C are sectional views of steps in utilizing an exemplarytissue anchoring catheter 440 through the sleeve-like annuloplasty ring400 to install one of the anchors 428. The anchoring catheter 440 issimilar to the anchoring catheter described above with respect to FIGS.3-4, with an assembly of components on the distal end thereof forregulating the pressure of the catheter against tissue. The componentsinclude a distal tubular housing 452 that slides axially within atubular housing frame 454 that is in turn surrounded by a thin tubularcover 456. A distal end of an elongated pusher 460 engages via a coilspring 462 a proximal end of the housing frame 454. The coil spring 462is centered on a short radially recessed portion 463 of the pusher 460and extends between the pusher and a proximal end of the tubular housing452. The distal end of the pusher 460 may be fixed with respect to thehousing frame 454, as well as to the proximal end of the coil spring462.

The tubular housing 452 includes an enlarged distal tip 464 formed as athick echogenic ring, such as by providing changes in diameter, chamfersor knurling on an exterior periphery thereof, as shown. (As explainedabove, “echogenic” does not strictly refer to the sound reflectiveproperties of the distal tip 464, but to its ability to effectivelyreflect various types of waves, such as the X-rays used in fluoroscopy.)

After positioning the next segment of the annuloplasty ring 400 to beinstalled against the annulus, as seen in FIG. 24A, the operatoradvances the catheter 440 and connected housing frame 454 to compressthe spring 462, as seen in FIG. 24B. Although not shown, the pusher 460preferably extends back to a proximal handle and an actuator whichslides it forward and backwards, or is coupled to a secondary shaft (notshown) which extends proximally to the handle. At the point where thespring 462 is fully compressed (or least compressed to a desiredamount), a distal portion of the housing frame 454 comes into closeproximity with the thick distal tip 464 of the tubular housing 452.

As with the earlier-described catheter, a schematic image of theappearance of the distal assembly of components in this sequence is seenin FIGS. 10A and 10B, wherein the relatively thick housing frame 454(54) shows up as a dark rectangular mass that eventually moves intoclose proximity with the relatively large mass distal tip 464 (64) thatalso shows up as dark on the image display. The remainder of the tubularcomponents have lesser wall thicknesses, and in contrast show up lessdistinctly on the image display. The operator can thus tell when thespring 462 has been fully compressed (or least compressed to therequisite amount), and the desired compressive force for anchordeployment has been reached. Several alternative configurations of adistal assembly of components on the catheter which affords goodvisibility using an imaging sensor/display are disclosed herein, some ofwhich are discussed above with regards to FIGS. 11 and 12.

As mentioned above, the coil spring 462 may be completely compressed, asshown, though this is not strictly necessary and the spring may be onlypartly compressed. In either case, compression of the spring 462 at themoment when the distal end of the housing frame 454 reaches the distaltip 464 provides a calibrated and desirable compressive force of thecatheter against the tissue. That is, the spring constant is calibratedso that linear compression to the extent seen in FIG. 24B produces acontact force which will ensure that the tissue anchor 428 will properlyembed within the tissue once advanced from the tubular housing 452. Aswill be understood, the particular contact force for which the spring462 is calibrated depends on a number of factors such as the size andconfiguration of the tissue anchor 428, the character of the tissue intowhich anchor is embedded, and the subsequent forces expected to beimparted to the annuloplasty ring 400 once fully implanted, amongothers. In an exemplary embodiment, the illustrated tissue anchor 428 isproperly anchored within the annulus tissue when expelled from thecatheter that exerts a contact force against the tissue of between0.5-2.0 N, and more preferably about 1.0 N.

Subsequently, as seen in FIG. 24C, the operator separately advances theflexible shaft 424 of the tool 420 through a lumen in the pusher 460.Although not shown, further advancement of the tissue anchor 428 causesit to pass through the fabric wall of the sleeve-like annuloplasty ring400 and contact the tissue, and it can then be rotated by the shaft 424and anchor driver 426 to cause the corkscrew-like tine to advance intothe tissue. Because of the compressive force imparted by the catheter440 on the tissue, an equal and opposite reactive force from the tissueis established. The tissue anchor 428 encounters this force uponemerging from the distal tip 464, and consequently deploys in theexpected manner.

While the foregoing is a complete description of the preferredembodiments of the invention, various alternatives, modifications, andequivalents may be used. Moreover, it will be obvious that certain othermodifications may be practiced within the scope of the appended claims.

What is claimed is:
 1. A method for ensuring secure anchoring of acardiac tissue anchor within cardiac tissue in a patient's body,comprising: advancing into the patient's body a distal end of anelongated flexible catheter of a cardiac tissue anchor deploymentsystem, the system including a proximal handle connected to thecatheter, the catheter having a lumen within which translates anelongated tissue anchor tool with a distal tissue anchor thereonsuitable for piercing and anchoring into cardiac tissue, the systemfurther including a tissue contact indicator assembly located adjacentthe distal end of the catheter and configured to be visible from outsidethe body on a display for an imaging sensor, the indicator assemblyhaving first and second relatively movable members, the indicatorassembly being configured to present a first visual image on the displayprior to contact between the distal end of the catheter and the cardiactissue and with the first and second relatively movable members in afirst relative position, and the indicator assembly being configured topresent a second visual image distinct from the first visual image afteradvancing and pressing the catheter against the cardiac tissue until apredetermined pressure is applied between the distal end of the catheterand the cardiac tissue and the first and second relatively movablemembers are in a second relative position; advancing the distal end ofthe catheter into contact with the cardiac tissue; advancing thecatheter toward the cardiac tissue such that the tissue anchor piercesinto the cardiac tissue and the first and second relatively movablemembers move with respect to each other from the first relativeposition; observing the display while advancing the catheter; haltingadvancement of the catheter when the display shows the first and secondrelatively movable members in the second relative position signalingthat a predetermined pressure has been applied between the distal end ofthe catheter and the cardiac tissue, the predetermined pressure beingcalibrated to ensure that the tissue anchor securely embeds into thecardiac tissue; and retracting the catheter leaving the tissue anchoranchored into the cardiac tissue.
 2. The method of claim 1, furtherincluding visualizing the distal end of the catheter as well as thecardiac tissue from outside the body, and repositioning the distal endof the catheter after advancing the distal end of the catheter intocontact with the cardiac tissue to place the distal end of the catheterinto contact with a different location on the cardiac tissue.
 3. Themethod of claim 1, wherein the distal end of the catheter terminates ina tubular housing having a thick-walled distal end that is visible tothe imaging sensor and defining the first relatively movable member, thetubular housing being arranged to slide proximally within the catheter,and the second relatively movable member comprises a tubular ring on thecatheter that is visible to the imaging sensor proximal to thethick-walled distal end, and the system includes a spring positionedbetween the tubular housing and a pusher within the catheter such thatadvancement of the pusher and catheter both advances the tubular ringrelative to the thick-walled distal end of the tubular housing andcompresses the spring, and an amount of spring compression determinesthe predetermined pressure.
 4. The method of claim 3, wherein thethick-walled distal end exhibits at least one chamfer or an outersurface that is echogenic.
 5. The method of claim 3, further including atensioner positioned intermediate the tissue contact indicator assemblyand the proximal handle which exerts a proximal force on the elongatedtissue anchor tool, the tissue anchor having a size that interferes witha portion of the tubular housing so as to retract the tubular housingwithin the catheter.
 6. The method of claim 1, wherein the firstrelatively movable member comprises a first radiopaque band thereon thatis more visible to the imaging sensor than a remainder of the movablemember, and the distal end of the catheter terminates in a tubularhousing having a second radiopaque band thereon which forms the secondrelatively movable member, wherein the first visual image shows thefirst and second radiopaque bands spaced a first distance apart and thesecond visual image shows the first and second radiopaque bands closertogether than the first distance.
 7. The method of claim 1, wherein thefirst relatively movable member comprises a first series of spaced apartradiopaque bands thereon that are more visible to the imaging sensorthan a remainder of the movable member, and the distal end of thecatheter terminates in a tubular housing forming the second relativelymovable member having a second series of spaced apart radiopaque bandsthereon, wherein the first visual image shows the first and secondseries of spaced apart radiopaque bands axially offset from each otherso that the display shows both series, and the second visual image showsthe first and second series of spaced apart radiopaque bands aligned sothat the display shows spaces between the aligned bands.
 8. The methodof claim 1, further including a locking member that prevents relativemovement of the first and second relatively movable members and ismanually disengaged using an actuator on the proximal handle.
 9. Themethod of claim 1, wherein the elongated tissue anchor tool comprises aflexible rail affixed to the tissue anchor, and the method includesattaching the flexible rail to an implant in the body.
 10. The method ofclaim 1, wherein the elongated tissue anchor tool is detachable from thetissue anchor, and the method includes detaching the elongated tissueanchor tool from the tissue anchor.
 11. A method for ensuring secureanchoring of a cardiac tissue anchor within cardiac tissue in apatient's body, comprising: advancing into the patient's body a distalend of an elongated flexible catheter of a cardiac tissue anchordeployment system, the system including a proximal handle connected tothe catheter, the catheter having a lumen within which translates anelongated tissue anchor tool with a distal tissue anchor thereonsuitable for piercing and anchoring into cardiac tissue, the systemfurther including a tissue contact pressure regulator assembly adjacentthe distal end of the catheter having a pusher shaft that is in a firstposition prior to contact between the distal end of the catheter and thecardiac tissue and the pusher shaft is coupled to move with the tissueanchor tool, the tissue contact pressure regulator assembly including aspring positioned between the pusher shaft and the distal end of thecatheter; advancing the distal end of the catheter into a first positionin contact with the cardiac tissue; advancing the pusher shaft todisplace the tissue anchor tool to the distal end of the catheter andcompress the spring to apply a force between the distal end of thecatheter and the cardiac tissue and so the tissue anchor pierces intothe cardiac tissue; further advancing the pusher shaft to a secondposition and embed the tissue anchor into the cardiac tissue, whereinthe spring is calibrated to apply a predetermined maximum force to thetissue anchor tool and ensure that the tissue anchor securely embedsinto the cardiac tissue; and retracting the catheter leaving the tissueanchor anchored into the cardiac tissue.
 12. The method of claim 11,wherein the spring is fully compressed when the pusher shaft is in thesecond position and remains stationary during further advancement of thetissue anchor tool.
 13. The method of claim 11, wherein the distal endof the catheter comprises a distal tubular housing having a relativelythin-walled body and a distal ring that is thicker than the thin-walledbody and consequently more visible on a display for an imaging sensorlocated outside the body, the tubular housing being arranged to slideproximally within the catheter, and the catheter having a tubularhousing frame at a distal end with a relatively thick wall that isvisible to the imaging sensor, wherein proximal movement of the distaltubular housing causes the distal ring to move into proximity with thetubular housing frame that is visible from outside the body on thedisplay for the imaging sensor.
 14. The method of claim 13, furtherincluding a tensioner positioned intermediate the tissue contactpressure regulator assembly and the proximal handle which exerts aproximal force on the elongated tissue anchor tool, the tissue anchorhaving a size that interferes with a portion of the tubular housing soas to retract the tubular housing within the catheter.
 15. The method ofclaim 13, further including a locking member that prevents movement ofthe tubular housing and is manually disengaged using an actuator on theproximal handle.
 16. The method of claim 11, wherein the elongatedtissue anchor tool comprises a flexible rail affixed to the tissueanchor, and the method includes attaching the flexible rail to animplant in the body.
 17. The method of claim 11, wherein the elongatedtissue anchor tool is detachable from the tissue anchor, and the methodincludes detaching the elongated tissue anchor tool from the tissueanchor.
 18. The method of claim 11, wherein the spring is a coil springpositioned around a narrow distal end of the pusher shaft that engagesthe catheter and compresses as the narrow distal portion passes throughthe catheter.
 19. The method of claim 11, further including a guideballoon positioned around the distal end of the catheter that helpsprevent entanglement of the distal end of the catheter with anatomicalstructures.